Bush made a judgment call based on intelligence information. THAT is not flip-flopping.
What happened in 1941 in Pearl Harbor? Was intelligence information on Japan's military movements and motivations dead on accurate?
How about the Cuban Missile Crisis? There was plenty of information made available to JFK that would have prevented the scandal OR at least allowed him to make a move MONTHS prior to when he did. Why did Kennedy wait until last minute?
Both of these Presidents, JFK and FDR are considered great men, and excellent Presidents. But both dropped the ball. It happens. There is no perfect President.
At this point, neither of these things matter. It's very easy to play Monday morning quarterback; the problem with Kerry is that he has (throughout his entire tenor in the Senate, spanning more then two decade) continually played Monday morning quarterback on every issue (even his own). Yet rarely does Kerry have a solution to move forward. He's putting on a good front for this Presidential Campaign. He has convinced democrats that he actually has ideas and solutions, and has his whole life.
The fact is, if Kerry is so good at coming up with solutions, were is his name on countless pieces of legislation? After two decades, you'd think his name would be all over the place, bills and proposals and such. After two decades in the Senate, you'd think that you would have risen up to be a leader in your party. Less than a year ago, most people, when asked about John Kerry, would have responded, "John who?"